1. Field of the Invention
This invention is in the field of galvanic electrochemical cells used to convert chemical energy into electrical energy (e.g. fuel cells) or store electrical energy as chemical energy (e.g., batteries and flow cells) having means to provide relative motion between an electrode and an electrolyte—including means for creating Taylor Vortex Flows (TVF) and Circular Couette Flows (CCF) in the electrolyte (U.S. Class 429/67,454; Int. Class H01M-2/38) to achieve accelerated chemical reaction rates in electrolytes containing faradaic or catalytic flakes (U.S. Class 429/105; Int. Class H01M-4/36).
2. Description of Related Art
Galvanic electrochemical cells include fuel cells used to convert chemical energy into electrical energy as well as batteries and flow cells used to store electrical energy in chemical form through reversible reactions (secondary cells) or irreversible reactions (primary cells). Their electrodes contain faradaic materials that support reduction-oxidation (redox) chemical reactions at the electrodes. Galvanic cells produce spontaneous reactions and are distinguished from electrolytic electrochemical cells that require electrical energy to initiate and sustain electrochemical reactions (e.g., electrowinning) that are usually irreversible. Also, electrolytic cell electrodes do not contain faradaic materials.
As used here, the term galvanic materials includes faradaic materials that support reduction-oxidation (redox) reactions and catalytic materials. In general, galvanic cells comprising, in one case, a pair of electrodes comprising faradaic materials that promote two (metal-electrolyte) or, in another case, three (catalyst-fuel or oxidizer-electrolyte) phase electrochemical reactions that separate electrons or ions from atoms or molecules, which then become energized ions (e.g., protons). The electrons travel from one electrode to the other electrode through an external electrical circuit where work is performed while the ions travel through a fluid electrolyte between the electrodes. This invention focuses on improving galvanic cell performance by providing novel means for enhancing electrolyte performance to lower loss of energy by ions transiting fluid electrolytes or by electrons entering electrodes—especially in non-Newtonian fluids.
Fluid electrolytes include aqueous alkaline solutions (e.g., KOH), aqueous acid solutions (e.g., H2SO4), carbonates (e.g., propylene carbonate) and organics (e.g., dimethylformamide). In many cases, these electrolytes are classified as Newtonian fluids; that is, their viscosities do not change as a function of shear rate.
Ion movement through electrolytes between the electrodes in many galvanic cells proceeds only under the influence of diffusion, migration and electric field gradients. A few cells pump electrolyte, which introduces convection gradients that are many times those of other gradients; but, may cause energy dissipating turbulent flows as pumping rates increase. My introduction of means for generating laminar highly correlated Taylor Vortex Flows (TVF) and Circular Couette Flows (CCF) in fuel cells (Cases A and D) and batteries (Case E) taught how to create very large convection gradients with high-shear-rate laminar electrolyte flows that accelerate galvanic reactions. The disclosed embodiments used KOH—a Newtonian fluid—as electrolytes; although no such limitation was taught.
Patent Publication No. US2010/0047671 of 25 Feb. 2010 to Chiang et al for a High Energy Density Redox Flow Device; Patent Publication No. US2011/0189520 of 4 Aug. 2011 to Carter et al for a High Energy Density Redox Flow Device; Patent Publication No. US2011/0200848 of 18 Aug. 2011 to Chiang et al for a High Energy Density Redox Flow Device and Duduta et al, Semi-Solid Lithium Rechargeable Flow Battery, Advanced Energy Materials (20 May 2011), Vol. 1, pp. 511-516, teach electrochemical flow cells containing a pair of high volumetric energy density fluid electrolytes that have high molar faradaic material content (i.e., 10-molar or greater). One electrolyte incorporates positive faradaic particles (catholyte) and while the other electrolyte contains negative faradaic particles (anolyte). The catholyte and anolyte each act as electrodes in promoting redox reactions when pumped through individual reaction chambers—each comprising an electric current collector connected to an external electrical circuit.
High volumetric energy density fluid electrolytes containing high-molar-concentrations of galvanic particles are non-Newtonian fluids. They can be or can contain colloidal suspensions (sols), slurries, gels, emulsions, micelles or thixotropic fluids. Their viscosities may remain constant or may change when pumped through a cell. For example, the viscosity of a thixotropic fluid will decrease at higher shear rates in a shear gradient flow field or over time at a constant shear rate while the viscosity of an anti-thixotropic fluid will increase under the same conditions.
In several prior art embodiments, the positive and the negative faradaic solubles or particles are each, respectively, dissolved or suspended in a solvent common to both electrolytes to provide catholytes and anolytes—each containing its own polarity of faradaic ions. Then the catholyte is pumped into or past a cathode while the anolyte is pumped through or past an anode. The electrolytes are prevented from mixing by a membrane or filter that permits ions and, in some cases, solvent to pass; but, blocks the passage of faradaic particles.
Chiang et al teach that the filter keeps the catholyte and anolyte faradaic particles separate; but, not the electrolyte when shared by both chambers. By contrast, one embodiment of my Case E (shown as FIG. 5) teaches a battery containing an ion-membrane that is not porous to two dissimilar electrolytes. The membrane of my Case E is specifically semi-permeable to lithium ion and nothing else, especially electrolyte.
Chiang et al teach that the faradaic particles reside in their separate electrolytes and not in electrodes. The particles, themselves, form the cell's electrodes. These electrodes are described as semi-solid or condensed ion storing liquid reactant ('848 at ¶[0012]). Chiang et al then state:                By “semi-solid” it is meant that the material is a mixture of liquid and solid phases, for example, such as a slurry, particle suspension, colloidal suspension, emulsion, gel, or micelle. “Condensed ion-storing liquid” or “condensed liquid” means that the liquid is not merely a solvent as it is in the case of an aqueous flow cell catholyte or anolyte, but rather, that the liquid is itself redoxactive. Of course, such a liquid form may also be diluted by or mixed with another, non-redox-active liquid that is a diluent or solvent, including mixing with such a diluent to form a lower-melting-temperature liquid phase, emulsion, or micelles including the ion-storing liquid.Therefore, these “semi-solid” and “condensed ion-storing liquid” electrolytes are non-Newtonian fluids (Duduta et al, FIG. 2, p. 513) that act as prior art electrodes because they can initiate redox reactions with fuels (e.g., H2) and oxidizers (e.g., O2) in fuel cells and sustain faradaic reactions in batteries and flow cells. These characteristics permit the use of simple, easy-to-construct electric current collectors in place of complex, expensive porous electrodes.        
However, there is a price to pay when using “semi-solid” and “condensed ion storing” electrolytes as taught by Chiang et al and Duduta et al; namely, a need for an electrolyte pump to provide a convection gradient that can overcome electrolyte viscosity, which is a major concern for their long, narrow electrolyte chambers. These electrolytes contain a mixture of faradaic particles (e.g., LiCoO2) and carbon particles (e.g., KETJENBLACK® porous electroconductive carbon particles) that can transfer charges from the faradaic materials to the current collectors.
The Chiang et al and the Duduta et al electrochemical processes proceed by promoting a faradaic reaction at the surface of a faradaic particle that creates an electron or a hole (absence of electron) and the necessary simultaneous release or acquisition of an ion at the particle surface. In the case of an electron, the reaction can only proceed by attracting the electron to move from the faradaic particle surface to a nearby conductor, which may be the current collecting electrode metal surface or a carbon particle in contact with that surface. The released positively-charged ion is then free to move through the electrolyte solvent toward the other electrode. However, electron and hole transfers during random momentary contact between freely-suspended faradaic and carbon particles while either are in mutual contact with the metal surface is limited to a small percentage of collisions.
In the Chiang et al and the Duduta et al cells, a freely suspended faradaic particle must come into contact with a metal electric current collector that can transfer the electron to an external circuit. A freely-suspended carbon particle can only act as a conduit for electrons upon collision with the faradaic particle if it is itself in contact with a metal electric current collector. Since the diffusion, concentration and migration gradients for either particle in the electrolyte are small, a pump is required both to overcome fluid drag caused by long, narrow electrolyte chambers and to force the charged carbon or faradaic particle to contact the electric current collector. Chiang et al also teach a need for small-diameter chambers of 1 cm to 100 micrometers; probably, to increase the rate at which the several particles contact the chamber's walls and transfer their charges. A similar process—but in reverse—moves an electron from a carbon particle to fill a hole or electron vacancy.
An increase in pumping rate is effective in increasing cell electric current up to a point where turbulence occurs. Further increases in the pumping rate cause a decrease in cell electric current. My invention that is described below teaches how to overcome the limitations of galvanic cells (e.g., fuel cells, batteries, flow cells) through the use of TVF, CCF and improved high-molar, non-Newtonian electrolytes that contain novel particles.